1. Field of the Invention
This invention relates to a method for the production of a graft resin composition having a vinyl compound grafted to a propylene polymer useful as adhesive agent, coating agent, modifying agent, micro-dispersing agent, polymer-alloying agent, functional forming material, and macromolecular compatibility-imparting agent.
2. Prior Art Statement
Heretofore, for the purpose of imparting improved rigidity, dimensional stability, and printability, for example, upon the propylene polymer as a molding material, an attempt has been made at adding to the propylene polymer a vinyl polymer such as, for example, polystyrene and further an organic peroxide as a cross-linking agent or a grafting agent and blending them in a molten state (Japanese Patent Public Disclosure No. SHO 61(1986)-127714).
A propylene polymer has been proposed which is produced by a method of graft polymerizing styrene onto a propylene polymer through the agency of an ionizing radiation. This method has been found to be fairly effective in uniformly dispensing polystyrene in the propylene polymer.
The method of solution graft polymerization which makes use of such a solvent as xylene or toluene and the method of emulsion graft polymerization are also known to the art.
It has been also proposed to produce a graft resin composition by impregnating propylene polymer particles with a vinyl monomer and polymerizing the impregnated particles in an aqueous suspension system (Japanese Patent Publication SHO 58(1983)-53003). This method produces better results than the other methods, as shown by the fact that the resin composition obtained in consequence of the polymerization has the vinyl polymer uniformly distributed therein.
These methods have faults of their own as follows.
The propylene polymer and a styrene type polymer are substantially incompatible with each other. Even an attempt at blending these two polymers in the presence of an organic peroxide as a grafting agent brings about absolutely no grafting effect. In the cicumstances, the practice of using more than 10% by weight of a styrene type polymer in the blend has never been realized. Generally, the blend has barely permitted incorporation therein of 0.2 to 5% by weight of a styrene type polymer. Even when the blend incorporates the styrene type polymer in such a small amount as described above, the shaped article made of this blend exhibits insufficient shock resistance and possesses poor appearance because the two component polymers have substantially no compatibility with each other.
Since the exposure of the polymerization system to the ionizing radiation must rely on a special process called the radiation graft polymerization method, it is not fully feasible from the economic point of view. Further since the reaction induced by this method occurs only in the surface region of the whole mass of the reaction system, the amount of styrene to be introduced into the produced blend has its limit.
In the solution graft polymerization method, because of the solubility of the propylene polymer, the propylene polymer must undergo polymerization as diluted with a large volume of a solvent. This method, therefore, has the disadvantage that the chance for mutual contact among the vinyl monomer, the polymerization initiator, and the propylene polymer is small and the efficiency of reaction of vinyl monomer is poor. It also proves to be disadvantageous economically because aftertreatments such as for recovery of solvent are complicated. In the case of the method of emulsion graft polymerization, since the reaction is limited to the surface region of the propylene polymer particles, this method has a disadvantage that the product thereof suffers from poor homogeneity.
By the polymerization which is carried out in an aqueous suspension system, there is obtained a resin composition in which the vinyl polymer is thoroughly dispersed. This resin composition, however, does not necessarily enjoy appreciably high grafting efficiency because the composition is formed mainly by physical entanglement of the propylene polymer and the vinyl polymer. When the resin composition is heated or caused to contact a solvent in the course of secondary fabrication, therefore, the vinyl polymer particles uniformly dispersed in the resin composition tend to undergo secondary agglomeration. This adverse phenomenon is a serious problem when the resin composition is to be used as a functional molding material or as a macromolecular compatibility-imparting agent.
The inventors conducted a study in search of a method for the production of a resin composition having a propylene polymer and a vinyl polymer dispersed in a matrix in such a manner that the polymer components of the dispersed phase thereof will exhibit a high grafting efficiency to the matrix component and will refrain from undergoing secondary agglomeration in the course of the secondary fabrication of the resin composition. They have consequently found that the graft resin composition aimed at can be obtained by first preparing a specific graft precursor and then causing the graft precursor, either directly or subsequently to addition thereto of a specific polymer, to be kneaded in a melted state. This invention has been perfected as a result.